externals/grill/fftease/src/fold.c


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/*
 * multiply current input I by window W (both of length Nw);
 * using modulus arithmetic, fold and rotate windowed input
 * into output array O of (FFT) length N according to current
 * input time n
 */
void fold( float *I, float  *W, int Nw, float *O, int N, int n )
{
 
    int i;

    for ( i = 0; i < N; i++ )
	O[i] = 0.;

    while ( n < 0 )
	n += N;
    n %= N;
    for ( i = 0; i < Nw; i++ ) {
	O[n] += I[i]*W[i];
	if ( ++n == N )
	    n = 0;
    }
}